1. The Field of the Invention
The present invention relates generally to a current-perpendicular-to-plane (CPP) read head for magnetic recording and, in particular, to a CPP read head with an amorphous magnetic bottom shield layer and an amorphous nonmagnetic bottom lead layer.
2. The Relevant Art
Computer systems generally utilize auxiliary memory storage devices having magnetic read/write heads and a magnetic medium. Data can be written on the magnetic medium by the magnetic write head and can be read from the magnetic medium by the magnetic read head. A direct access storage device, such as a disk drive, incorporating rotating magnetic disks is commonly used for data in magnetic media on the disk surfaces. Data are written on concentric, radially spaced tracks on the magnetic media, and are read from the tracks on the magnetic media.
In high capacity disk drives, a current-in-plane (CIP) read head, in which a sense current flows in a direction parallel to film interfaces, is now extensively used to read data from the tracks on the magnetic media. This CIP read head comprises a giant magnetoresistance (GMR) sensor, a longitudinal bias (LB) stack, and conductor leads. The GMR sensor typically comprises two ferromagnetic films separated by an electrically conducting nonmagnetic film. The resistance of this GMR sensor varies as a function of the spin-dependent transmission of conduction electrons between the two ferromagnetic films and the accompanying spin-dependent scattering which takes place at interfaces of the ferromagnetic and nonmagnetic films.
In the conventional GMR sensor, one of the ferromagnetic films, referred to as a transverse pinned (or reference) layer, typically has its magnetization pinned by exchange coupling with an antiferromagnetic film, referred to as a transverse pinning layer. The magnetization of the other ferromagnetic film, referred to as a free (or sense) layer is not fixed, however, and is free to rotate in response to signal fields from the magnetic medium. In this GMR sensor, a GMR effect varies as the cosine of the angle between the magnetization of the reference layer and the magnetization of the sensing layer. Data can be read from the magnetic medium because the external magnetic field from the magnetic medium rotates the magnetization of the sense layer, which in turn changes the resistance of the GMR sensor and correspondingly changes a readout voltage.
FIG. 1 shows a typical prior art CIP read head 100. A GMR sensor portion 101 is fabricated in a central region 102, while LB (longitudinal bias) stacks and conductor lead layers 126 are fabricated in two end regions 103 and 105. Various films of the GMR sensor are deposited on a bottom gap layer 118, which is previously deposited on a bottom shield layer 120. The bottom shield layer 120 is deposited on a wafer.
Photolithographic patterning and ion milling are applied to define the central region 102 and the two end regions 103 and 105. In the GMR sensor 101, a ferromagnetic sense layer 106 is separated from a ferromagnetic reference layer 108 by an electrically conducting nonmagnetic spacer layer 110. The magnetization of the reference layer 108 is fixed through exchange coupling with an antiferromagnetic transverse pinning layer 114. The depicted GMR sensor 101 also comprises seed layers 116 and cap layers 112. The seed layers 116 facilitate the growth of the transverse pinning, reference, spacer and sense layers with preferred crystalline textures during depositions so that desired improved GMR properties are attained. The cap layer 112 protects the underlying films from oxidation during subsequent annealing operations.
The LB stacks and conducting lead layers 126 are deposited in the end regions 103 and 105. The films deposited in the central and end regions are sandwiched between electrically insulating nonmagnetic films, one referred to as a bottom lead layer 118 and the other referred to as a top lead layer 124.
To ensure proper sensor operation, exchange coupling between the transverse pinning layer 114 and the reference layer 108 must be sufficiently high to rigidly pin the magnetization of the reference layer 108 in a transverse direction perpendicular to the air bearing surface (the surface being viewed in FIG. 1). An inadequate exchange coupling may cause canting of the magnetization of the reference layer from the preferred transverse direction, thus causing malfunction of the GMR sensor. This ferromagnetic/antiferromagnetic exchange coupling is typically characterized by a unidirectional anisotropy field (HUA) induced by this exchange coupling. This HUA field thus must be sufficiently high to rigidly pin the magnetization of the reference layer for proper sensor operation.
To ensure optimal biasing of GMR responses, another exchange coupling between the ferromagnetic reference layer and the ferromagnetic sense layers must be optimized in order to orient the magnetization of the sense layer in a longitudinal direction parallel to the air bearing surface. The ferromagnetic/ferromagnetic exchange coupling is typically characterized by a ferromagnetic field (HF) induced by the exchange coupling. The HF field thus must be very well controlled in order to balance two other fields in the sense layer, a demagnetizing field induced by the magnetization of the reference layer, and a current-induced field. A non-optimal or high HF may cause the magnetization of the sense layer to deviate from the preferred longitudinal direction, thus leading to non-linear, low GMR responses.
The disk drive industry has been engaged in an on-going effort to fabricate a narrower GMR sensor for increasing disk drive track density, and to sandwich the CIP read head into thinner gap layers for increasing linear density. It is crucial for the narrower GMR sensor to exhibit a higher GMR coefficient, and for the thinner gap layer to prevent current shorting between the CIP read head and shield layers. The GMR coefficient of the GMR sensor is expressed as xcex94RG/R//, where R// is a resistance measured when the magnetizations of the sense and reference layers are parallel to each other, and xcex94RG is the maximum giant magnetoresistance (GMR) measured when the magnetizations of the sense layer 106 and the reference layer 108 are antiparallel to each other. A higher GMR coefficients leads to higher signal sensitivity.
A new challenge will be posed when increasingly narrow GMR sensors cannot be made to exhibit higher GMR coefficients for further increasing the track density, and when increasingly thinner gap layers cannot be made to prevent current shorting between the CIP read head and shield layers. To solve these issues, a current-perpendicular-to-plane (CPP) read head, which also comprises layers of deposited films but in which the sense current flows in a direction perpendicular to the film interfaces, has been developed.
CPP read heads typically also comprise a GMR sensor, a LB stack, and conductor leads, but all these films are confined in the central region only. The conducting spacer layer separating the reference and sensing layers is, in the CPP read head, used as a conducting barrier layer across which the sense current flows. Typically, the GMR sensor of the CPP read head exhibits a GMR coefficient that is about 40% higher than a similar GMR sensor of the CIP read head. In addition, the GMR sensor can be replaced by a tunneling magnetoresistance (TMR) sensor by replacing the conducting barrier layer with an insulating barrier layer. Typically, the TMR sensor exhibits a tunneling magnetoresistance (TMR) coefficient higher than the GMR sensor of the CPP read head. The TMR coefficient of the TMR sensor is expressed as xcex94RT/R//, where R// is a resistance measured when the magnetizations of the sense and reference layers are parallel to each other, and xcex94RT is the maximum tunneling magnetoresistance (TMR) measured when the magnetizations of the sense and reference layers are antiparallel to each other. A higher TMR coefficients leads to higher signal sensitivity.
FIG. 2 shows a typical prior art CPP read head 200. Bottom leads 218, the GMR (or TMR) sensor 201, the LB stack 225, and top leads 228 are all fabricated in a central region 202, while only insulating gap layers are formed in two end regions 203 and 205. Various films of the bottom leads 218, the GMR (or TMR) sensor 201, the LB stack 225, and the top leads 228 are all deposited on a bottom shield layer 220 which is, in turn, deposited on a wafer (not shown). Photolithographic patterning and ion milling are applied to define the central region 202 and the two end regions 203 and 205. In the GMR (or TMR) sensor 201, a ferromagnetic sense layer 206 is separated from a ferromagnetic reference layer 208 by an electrically conducting (or insulating) nonmagnetic spacer layer 210.
The magnetization of the reference layer 208 is fixed through exchange coupling with an antiferromagnetic transverse pinning layer 214. The depicted GMR sensor 200 (and the similarly configured TMR sensor) also comprises a seed layer 216 and a decoupling layer 212. On the other hand, the LB stack 225 comprises a longitudinal pinned layer 224, a longitudinal pinning layer 220 and a cap layer 226.
Because the sense current flows from bottom shield layer 220, through the CPP read head 201, to the top shield layer 230, or vice versa, electrical shorting between the bottom shield layer 220 and the CPP read head 201, and between the CPP read head 201 and the top shield layer 230, is no longer a concern. As a result, the read gap thickness can be further decreased and consequently, the linear density can be further increased.
Issues are encountered when attempting to use the CPP read head to increase both the track and linear densities. The bottom shield layer is typically formed of a xcx9c1.75 xcexcm thick Fexe2x80x94Sixe2x80x94Al or Nixe2x80x94Fe polycrystalline film, while the bottom lead is typically made of a xcx9c30 nm thick Ta films. Their microstructures and rough topographies (mainly resulting from grain boundary grooves) may substantially affect the microstructures and flatness on the GMR or TMR sensor. These microstructural effects may lead to difficulties for the transverse pinning and reference layers to develop desired microstructures after annealing for attaining a high unidirectional anisotropy field (HUA). The rough topographies may lead to difficulties in achieving a barrier layer, formed of a xcx9c2 nm thick Cuxe2x80x94O conducting film in the GMR sensor (or formed of a xcx9c0.6 nm thick Alxe2x80x94O insulating film in the TMR sensor), with a desired flatness and a consequent low ferromagnetic coupling field (HF) and high GMR (or TMR) coefficient.
In the fabrication process of the prior art CPP read head, chemical mechanical polishing (CMP) is often applied to the bottom shield layer. Even after conducting a fine CMP process, the bottom shield layer still inevitably exhibits a rough topography due to an inherent polycrystalline nature. In the bottom shield layer, formed of a polycrystalline film, many grains with different crystalline orientations exist and may form grain boundaries with grooves due to different orientations. The existence of these grooves lead to the inherent rough topography.
From the above discussion, it can be seen that it would be a beneficial addition to the art to attain a controllable low HF and a high GMR (TMR) coefficient in a CPP read head by providing a bottom shield layer and a bottom lead with smooth topographies, on which the films of the GMR (or TMR) sensor can grow without unwanted microstructural effects.
The apparatus of the present invention has been developed in response to the present state of the art, and in particular, in response to the problems and needs in the art that have not yet been fully solved by a currently available CPP read head. Accordingly, it is an overall object of the present invention to provide an improved CPP read head that overcomes many or all of the above-discussed shortcomings in the art.
To achieve the foregoing object, and in accordance with the invention as embodied and broadly described herein in the preferred embodiments, an improved CPP read head is provided. The CPP read head preferably comprises a bottom shield layer formed of an amorphous magnetic material, together with a bottom lead layer formed of an amorphous nonmagnetic material disposed to one side of the bottom shield layer. The CPP read head also preferably comprises a transverses pinning layer disposed to one side of the bottom lead layer, a keeper layer disposed to one side of the transverse pinning layer, a reference layer disposed to one side of the keeper layer, and a sensing layer disposed to one side of the reference layer.
In preferred embodiments, the CPP read head also comprises an antiparallel-coupling (APC) layer formed of a nonmagnetic conducting film disposed to one side of the keeper layer and a barrier layer formed on a nonmagnetic film disposed to one side of the referenced layer.
Also included may be a decoupling layer formed of a nonmagnetic film disposed to one side of the sensing layer, a longitudinal pinned layer formed of a ferromagnetic film disposed to one side of the decoupling layer, and a longitudinal pinning layer formed of an anti ferromagnetic (AFM) film disposed to one side of the longitudinal pinning layer. A cap layer may also be formed of a nonmagnetic film and disposed to one side of the longitudinal pinning layer.
Preferably the shield layer is formed on a substrate from an Fexe2x80x94Alxe2x80x94Si or Nixe2x80x94Fe film.
The CPP read head of the present invention in one embodiment may also comprise a second shield layer formed of an amorphous film deposited on the shield layer.
The CPP read head of the present invention in this embodiment also preferably comprises a bottom lead formed of an amorphous film deposited on the second shield layer formed of the amorphous film. In an alternative embodiment, a reference layer may be formed of an amorphous film deposited on the transverse pinning layer.
The CPP read head of the present invention in a further alternative embodiment comprises a polycrystalline reference layer within which in-situ oxidation is applied for the formation an intermediate amorphous phase.
A fabrication method of the present invention is also presented for forming amorphous films used as the second shield layer, the bottom lead, and the reference layer.
These and other objects, features, and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.